The present invention relates to a holder for a lens system that is suited to an image displaying apparatus that magnifies and projects, onto a screen, an image from an image generating apparatus (for example, a light modulator such as a liquid crystal display device, a DMD, or the like), to a lens unit comprising such lens system, and to an image displaying apparatus comprising such lens unit.
A lens unit used in apparatus (for example, a camera, projector, or the like) is produced by holding a plurality of lenses in a cylindrical holder or lens holding unit, and is incorporated in the apparatus. Japanese Laid-Open Patent Publication No. 2002-40308 discloses an apparatus where contact surfaces are formed interior of cylindrical lens holding members, lenses are inserted into the lens holding members and the lenses are fixed using pressing rings in a state where the edges of the lenses contact the contact surfaces respectively. According to this construction, a plurality of lenses are assembled in one unit in a state where the distances between the lenses in the direction of the optical axis are fixedly adjusted.
When constructing an optical system (lens unit) from a plurality of lenses, tolerances for the thicknesses of the lenses affect the image forming performance and aberration correction. The effect on the performance of the lens unit is unequal for the front and rear (i.e., front and rear surfaces) of each lens included in the lens unit. Due to factors such as a difference in curvature between the front and rear surfaces of a lens and/or the relationship with adjacent lenses or lens groups, there is a difference between the effect of the tolerance for one surface of a lens and the effect of the tolerance for the other surface of the lens.
In the lens apparatus disclosed by Japanese Laid-Open Patent Publication No. 2002-40308, the positions of the one side of the lens surfaces that contacts the contact surface of a lens holding member is precisely determined. If the lenses had different diameters and were inserted into the lens holding member by a favorable order, for all of the lenses, the front or rear surface of each lens that has a large effect is placed in contact with the contact surface of the lens holding member to control the position of such surface.
However, for the lens apparatus that includes lenses of a similar diameter, it is difficult for precisely maintaining the distance between the facing surfaces of such lenses. When holding a plurality of lenses of a similar diameter, even if the order in which the lenses are inserted into the lens holding member is adjusted, it becomes difficult to support face to face surfaces that have a large effect using the contact surfaces.
There are known projectors that generate an image by modulating light from a light source using a light modulator (for example, light valve) such as a liquid crystal display or a DMD and magnify and project the image onto a screen using a lens unit. Rear projectors are one example of such projectors. Rear projectors project images from behind the screen, and show promise as slim image displaying apparatuses that display sharp images on a large screen. In a projector disclosed by Japanese Laid-Open Patent Publication No. 2001-222060, a projection unit that includes a projection lens and its incident side is fixed, using a supporting means, in a cantilever state to an optical unit that includes a light source and a liquid crystal display unit.
In a “front-type” projector where the screen is separated from the projector main unit and images are projecting onto the screen from the front, the position of some of the lenses in the lens unit, normally the lens closest to the screen, can be slightly adjusted to focus the image projecting onto the screen and produce a sharp image.
In a rear projector where images are projecting from behind the screen, the lens unit is housed inside a housing of the rear projector. Therefore, it is difficult for the user to make focus adjustments. So, projectors are shipped after the focus has been adjusted.
In a rear projector, the lens unit is housed in the housing together with the light source that becomes a source of heat. Therefore the temperature of the lens unit is susceptible to rising. Accordingly, for the lens unit of a rear projector, to attain sharper images and fairer optical performance such as focusing, more precise setting of the lens positions and less fluctuate to temperature fluctuations are required.